1. Field of the Invention
The present invention relates to a control system/method for controlling the disengagement of the friction master clutch in a vehicular automated mechanical transmission system and, in particular, to a control system/method for controlling disengagement of the master clutch at initiation of a shift from a currently engaged transmission ratio into a target transmission ratio or transmission neutral.
2. Description of the Prior Art
Vehicular fully or partially automated mechanical transmission systems are well known in the prior art. Examples of such transmission systems may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,648,290 and 4,850,236, the disclosures of which are incorporated herein by reference.
Briefly, vehicular automated transmission systems comprise a fuel controlled engine, a multiple speed mechanical transmission and a selectively engaged and disengaged master friction clutch drivingly interposed between the engine and transmission. For more rapid downshifts, a downshift or input shaft brake is usually provided and, for more efficient vehicle retardation, an engine exhaust brake may be provided. A control unit, typically a microprocessor based ECU, receives a plurality of input signals, processes the input signals according to predetermined logic rules and issues command output signals to various actuators such a fuel controller, a clutch operator, an input shaft brake operator and/or a transmission operator.
The prior art fully or partially automated mechanical transmission systems typically operate in a shift sequence wherein the master clutch is disengaged at initiation of shifting to assure disengagement of the positive jaw clutches associated with the currently engaged ratio. Disengagement of the master clutch, if premature or when the engine brake is applied, may result in an undesirable rapid yaw in the vehicle cab as torque in the drive line unwinds with disengagement of the master clutch. This reaction, commonly referred to as "cab lurch" or "cab dip" is particularly disagreeable if the master clutch is disengaged at relatively high fueling of the engine, relatively high torque in the driveline and/or when an engine brake is not fully disengaged.